The present invention relates to an apparatus for controlling the temperature in an enclosure such as a passenger compartment of a motor vehicle.
Such a system typically comprises a heater and a cooler disposed in an air duct which opens into a vehicle passenger compartment. The heater and cooler are automatically controlled to maintain the temperature in the compartment at a desired set or command value. An air mix door or damper is provided to control the proportion of air flow through the heater and cooler.
Under low cooling load conditions, a compressor or an evaporator of the cooler are maintained on or the compressor is operated in an ON-OFF mode by a defroster switch having a constant changeover temperature level to maintain the temperature of air passing through the evaporator at a constant level. The air mix door mixes heated air from the heater with cooled air from the cooler to provide the desired compartment temperature.
It is not efficient to mix heated air with cooled air due to the irrational waste of power caused by the heater and cooler working against each other. The conventional prior art arrangement further wastes power since the compressor is operated more than necessary. The power wasted by the temperature control apparatus is produced by the engine, resulting in reduced vehicle performance and increased consumption of expensive fuel.